What you've said is: Looking only at the internalized costs, pointless-wasting a percentage of clothes costs X but reduces clothes cost in the store by Y, with Y being larger than X.
Okay. Irrelevant - that math doesn't include externalized costs. It may well be that this is a stupid idea, but "market decided destroying some clothes was more efficient" doesn't prove anything unless you can show that the size of the externalized costs to this process are 0 or close enough to 0 to have no meaningful relevance.
Or not. Who knows. The point is, this 'economically it is more efficient' is not a proven case because the externalities need to be taken into account, and so far the person I've been responding to seems to not understand this part, or is ignoring it.
Clothing is of course a bit easier to deal with (it'll still grow mildew if you don't protect it from moisture!), but the source link explicitly anticipates there will be some circumstances where it's impossible to give away clothing and authorizes destruction in that case.
This isn't some random guy. Their entire job is dealing with the logistics of big piles of clothes, and they have months in advance to plan.